Shape-transferring cannula system and method of use

ABSTRACT

A method for advancing a rigidizable medical device may include rigidizing a portion of an outer element of the device, and while the portion of the outer element is rigidized, advancing an inner element of the device relative to the outer element of the device by a first preestablished length of advancement. The method may also include, after advancing the inner element, relaxing the portion of the outer element of the device. The method may further include, after relaxing the portion of the outer element, advancing the outer element of the device relative to the inner element of the device by a second preestablished length of advancement.

RELATED U.S. PATENT APPLICATIONS

This application is a continuation of Ser. No. 13/632,478 (filed Oct. 1,2012; currently pending), which is a divisional of U.S. patentapplication Ser. No. 10/661,159 (filed Sep. 12, 2003; now U.S. Pat. No.8,298,161 B2), which claims the benefit of priority of U.S. ProvisionalApplication No. 60/409,927 (filed Sep. 12, 2002), the entirety each ofwhich is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to devices, systems, and processes usefulfor exploration of hollow body structures, particularly those areasaccessed through a tortuous, unsupported path. More particularly, thepresent invention relates to a shape-transferring cannula device thatcreates a custom-contoured access port for insertion and removal ofdiagnostic, surgical, or interventional instruments to and from a sitewithin the body to which the physician does not have line-of-sightaccess.

BACKGROUND OF THE INVENTION

Surgical cannulas are well known in the art. Such devices generallyinclude tube-like members that are inserted into openings made in thebody so as to line the openings and maintain them against closure.Surgical cannulae can be used for a wide variety of purposes, and theirparticular construction tends to vary accordingly (see, e.g., U.S. Pat.No. 5,911,714). Flexible endoscopes, endovascular catheters andguidewires, and trocar cannulae such as those used in laparascopicsurgery, are examples of such devices. Several U.S. patents recite suchdevices. See, for example, U.S. Pat. Nos. 5,482,029; 5,681,260;5,766,163; 5,820,623; 5,921,915; 5,976,074; 5,976,146; 6,007,519;6,071,234; and 6,206,872.

All of these devices are in use in one form or another and they arehelpful to some extent, but they also pose several problems. Flexibleendoscopes and endovascular catheters rely on reaction forces generatedby pushing against the tissue of the body cavity being explored tonavigate around corners or bends in the anatomy. This approach worksreasonably well for small-diameter endovascular catheters that aretypically run through arteries well supported by surrounding tissue. Inthis case the tissue is effectively stiffer than the catheter orguidewire and is able to deflect the catheter's path upon advancementinto the vessel. The approach is much less successful in the case offlexible endoscopes being guided through a patient's colon or stomach.In these cases the endoscope is either significantly stiffer than thebody cavity tissue it is being guided through or, as is the case for thestomach or an insufflated abdomen, the body cavity is sufficientlyspacious that the endoscope has no walls at all to guide it. In the caseof colonoscopy, the endoscope forces the anatomy to take painful,unnatural shapes. Often, the endoscope buckles and forms “loops” whenthe colonoscopist attempts to traverse tight corners. Pushing on the endof the flexible endoscope tends to grow the loop rather than advance theendoscope. “Pushing through the loop” relies on the colon to absorbpotentially damaging shapes of force to advance the endoscope. In casesof unusually tortuous anatomy, the endoscope may not reach its intendedtarget at all, leaving the patient at risk of undiagnosed andpotentially cancerous polyps.

Endovascular catheters have drawbacks as well. While generally flexibleenough to avoid seriously damaging the vessel's endothelial surface,guidewires are difficult to guide into small side branches of largevessels such as the coronary ostia or into relatively small vesselsconnecting to relatively large chambers such as the pulmonary veins.Catheters are even more limited in their ability to deal with greatlytortuous vessel anatomy such as the vessels radiating from the brain'sso-called Circle of Willis.

Ablation and EKG mapping catheters used in cardiologicalelectrophysiology find their intended targets chiefly by trial and errorinsertion and twisting of a guidewire/catheter accompanied by grossmotions of the entire catheter. A need, therefore exists for a cannulasystem that provides access port for insertion and removal ofdiagnostic, surgical, or interventional instruments to and from a sitewithin the body to which the physician does not have line-of-sightaccess. Furthermore, there is a need for cannula systems that can followa tortuous path through hollow soft-tissue structures without relying onthe surrounding tissue to mechanically support and guide its insertionand may be steered and advanced directly to an anatomical point ofinterest.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sectional view of the shape transferringcannula system illustrating the major components.

FIGS. 2A-2D illustrate diagrammatic sectional representations of asequence of rigidizing structure stiffening, relaxing, and advancementthat enables guiding of the shape transferring cannula.

FIG. 3 is a perspective view of an embodiment of laterally parallelrigidizing core and sheath linkage structures.

FIGS. 4A and 4B illustrate perspective views of captured-link rigidizinglinkages.

FIG. 5 is a perspective view of a cable-rigidized core linkage.

FIG. 6 shows perspective and sectional views of a cable-rigidized sheathlinkage.

FIG. 7 is a sectional view of an off-axis tensioning mechanism for acable-rigidized sheath linkage.

FIG. 8 is a perspective view of an alternate embodiment of a laterallyparallel sheath linkage.

FIG. 9 is a sectional view of a laterally parallel sheath linkage.

FIG. 10 shows perspective and end views of an open-sided sheath linkage.

FIG. 11 is a perspective view of a laterally parallel sheath linkagewith compliant elements.

FIGS. 12A-12H illustrate various views of an alternating advancementmechanism in accordance with the present invention.

FIGS. 13A-13C show perspective views of a rotating link cannulastructure

FIGS. 14A-14C show diagrammatic views of a cannula structure including apassive element.

FIG. 15 is a sectional view of a continuous stiffening cannulastructure.

FIG. 16 is a perspective view of a cannula structure formed withnormally-rigid, thermally relaxing materials.

FIGS. 17A and 17B illustrate sectional views of vacuum-stiffeningcannula structure elements.

FIG. 18 is a sectional view of a pressure-stiffening cannula structure.

FIGS. 19A and 19B show a sectional view of normally-rigid, vibrationallyrelaxing cannula structure elements.

FIGS. 20A and 20B illustrate sectional views of a cannula structureincluding active material elements.

FIG. 21 is a perspective view of two-axis pivoting links.

FIG. 22 depicts a catheter with a shape-transferring section.

FIG. 23 depicts a thermally relaxing normally-rigid structure.

FIG. 24 depicts a motorized advancement mechanism.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS

The present invention is directed to a novel shape-transferring cannulasystem, which provides access to tortuous and unsupported paths. Theshape-transferring cannula system and method enables exploration ofhollow body structures, and creates a custom-contoured access port forinsertion and removal of, for example, diagnostic, surgical, orinterventional instruments to and from a site within the body to whichthe physician does not have line-of-sight access.

The shape-transferring cannula can follow a tortuous path through hollowsoft-tissue structures without relying on the surrounding tissue tomechanically support and guide its insertion. The system includes twoparallel rigidizing sections that alternatingly stiffen and relax withrespect to one another and alternatingly transfer the path shapetraced-out by the articulating tip to one another. A steerablearticulated tip is attached to one of the rigidizing sections. Thecannula's custom shape is formed by guiding the articulated tip along adesired path direction, stiffening the attached rigidizing section, andadvancing the other rigidizing section along the stiffened section.

The end of the shape-transferring cannula may be steered and advanceddirectly to an anatomical point of interest. The user traces a path forthe shape-transferring cannula with the steerable tip and in doing sodefines the longitudinal shape assumed by the cannula, thus directingthe working end of the cannula to a target site without substantiallydisturbing the length of cannula behind it. The ability to navigatepredictably within heart chambers and swap out catheters from arelatively fixed position, for example, greatly improveselectrophysiologists' ability to methodically locate and ablate theectopic foci responsible for atrial fibrillation and other cardiacarrhythmias.

The ability to localize movements to the user-controlled tip of thecannula is especially valuable when working within particularlysensitive open structures such as the ventricles of the brain or looselysupported, tortuous structures such as the colon that provide verylittle mechanical support for intubation around corners.

The shape-transferring cannula system assumes the shape traced by thepath of the articulating tip in an incremental fashion, with the coreand sheath rigidizing structures transferring the traced path shape backand forth to each other. Having reached the target site, the externalsheath can be made flexible and slid out over the rigidized centralcore. Unlike the lengthy re-intubation procedure for a conventionalflexible endoscope, returning to the target site is simply a matter ofsliding the sheath or surgical instruments over the core that now actsas a guidewire. Alternately, the sheath may be left rigid and in placeonce having reached the target site and the core may be made flexibleand removed. This leaves the shaped sheath to act as a cannula throughwhich surgical instruments such as snares, ultrasound probes, biopsyprobes and other diagnostic devices, electrocautery tools, and the likemay be transferred to and from the target site.

The individual elements of the invention have useful applicationsindependent of the full system. For instance, the rigidizing sheathstructure may be used on its own as a rigidizing cannula when introducedto a target site by a conventional guidewire, flexible endoscope, orsimilar introduction element. Unlike conventional rigid cannulae, therigidizing cannula does not have a predetermined longitudinal shape.Yet, when stiffened, the rigidizing cannula may support reaction forceslike a rigid cannula when tools are run down its length, thus protectingsensitive tissue structures.

The present invention will now be described in detail with reference tothe following drawings. FIG. 1 depicts a preferred embodiment of ashape-transferring cannula system Id having two parallel rigidizing core1 and sheath 2 structures, a steerable articulated tip 3 attached to oneof the rigidizing structures, a proximal end 1 a, a distal end 1 b and alumen 1 c through which surgical tools may be introduced or throughwhich the target site may be irrigated or suctioned. The core 1 andsheath 2 are parallel structures that can be coaxial or side-by-side andthat may be made rigid or flexible with respect to one another. The coreand sheath structures may be unitary materials or continuous structures,or they can be formed of individual, flexibly connected rigid links. Thecore and sheath structure employs rigidizing cables which, when put intotension, pull the links together to increase friction between links andprevent relative motion between the links. The core's rigidizingstructure is built-up of links such that a convex spherical surface onone link engages a concave surface on an adjacent link. The core'srigidizing cable runs through each core link's central orifice,connecting the entire core rigidizing structure. The core link's centralorifice has a diameter D1 that is in the range from about 0.5 mm toabout 30 mm. Those of skill in the art will readily appreciate that theparticular application, e.g., device, to which the present invention isapplied may require a particular diameter D1, and it is within the scopeof the present invention to select an appropriate diameter D1 for thespecific application. For example, a typical endoscope employingstructures in accordance with the present invention may have an innerdiameter from about ¼ inch to about ½ inch, although larger or smallersizes may also be suitable.

The system employs a method of incremental advancement to deliver thedistal end 1 b of the cannula to a target site. The core 1 and sheath 2rigidizing structures are alternatingly advanced, one structure past theother, the stationary structure being made rigid and acting as a guidefor the advancing flexible structure. The steerable tip assembly 3 islocated on the end of at least one of the two rigidizing structures suchas the core 1 as depicted in FIG. 1. The steerable tip 3 may be actuatedvia cables or other tension members, magnetostrictive materials,bimetallic strips or other flexing elements, piezoelectric polymer filmsor ceramics, shape memory materials such as nickel-titanium shape memoryalloys or shape memory polymers, electroactive artificial musclepolymers, or the like. The length of the steerable tip 3 and the lengthL, described elsewhere herein, are preferably mutually selected to beabout the same length, so that the cannula can follow and track thesteerable tip (see FIG. 12G).

The overall length of the cannula will vary according to the particularhollow body structure for which it is intended. For instance, used in acolonoscope application the shape-transfer cannula length might rangefrom 100 cm to 180 cm. In a bronchoscope application the shape-transfercannula length might range from about 30 cm to about 100 cm. In acatheter application, the rigidizing core 1 and sheath 2 components of ashape-transfer cannula might be limited to a relatively small section ofthe entire catheter length, as depicted in FIG. 22. For example, thecore 1 and sheath 2 can be provided only at the distalmost end of thedevice or apparatus that is intended to be steered. In such a case themajority of the cannula's length might include “passive” conventionalextruded catheter material 251 and a non-rigidizing section of core 252.For example, in accessing particular areas within the heart'sventricles, the extra control provided by the shape-transferring core 1and sheath 2 components might only be needed within the ventriclesthemselves so the length of the rigidizing section R, need only besufficient to navigate within the ventricles themselves.

Another aspect of the present invention is that the distal, steerableportion of the apparatus has a shape-transforming length L and an outerdiameter D, with the ratio L/D being at least about 5 (L/D>5), so thatthere is enough longitudinal length of the shape-transforming portion ofthe device or apparatus to track the steerable tip 3.

FIG. 2 illustrates by way of example a sequence in which the core 1 andsheath 2 alternate sequentially between rigid and flexible such that theentire structure takes the shape traced by the steerable tip 3 as theshape-transferring cannula is inserted into a hollow body structure suchas the colon, stomach, lung bronchi, uterus, abdominal cavity, brainventricle, heart chamber, blood vessel, or the like. In FIG. 2 a, thesheath 2 is rigid and the core 1 with steerable tip 3 is flexible. Thesteerable tip 3 initially lies within and is approximately flush withthe distal end 1 b of the sheath 2 such that both the sheath 2 and core1 assume the same longitudinal shape whether curved or straight. Tobegin the sequence that advances and forms the longitudinal shape of theshaped cannula structure 1 d, in FIG. 2 b the core 1 is advanceddistally through the rigidized sheath 2, exposing the length of thesteerable tip 3. The user then directs the exposed steerable tip 3 inthe desired direction of insertion and advances the structure with, forexample, a squeeze advancement mechanism (which will be discussed laterherein) or through a cam mechanism or through any other structure ormechanism that rigidizes and relaxes the core 1 and sheath 2 in propersequence. Referring to FIG. 2 c, to advance the entireshape-transferring cannula structure 1 d, the core 1 is made rigid andthen the sheath 2 is relaxed and, as shown in FIG. 2 d, the sheath isadvanced over the core 1 and steerable tip 3. Preferably, thelongitudinal relative motion between the two rigidizing elements (i.e.core 1 and sheath 2) is limited to the length of the steerable tip 3,the user-controlled element that serves as the system's directionalguide. The sheath 2 is then made rigid and the core 1 is relaxed andadvanced to re-expose the steerable tip 3. Thus, in sequential fashion,the rigidizing structure portion of the shape-transferring cannula 1 dtakes the shape of the path traced by the steerable tip 3 as guided bythe user.

Other sequences and combinations of stiffening, flexibility, andadvancement to achieve the same result are possible within the scope ofthis invention. For instance, the sheath 2 and core 1 may benormally-stiff structures that momentarily become flexible atappropriate times in the shape-transferring cannula advancementsequence. In another example, the sheath 2 and core 1 may benormally-flexible structures that momentarily become rigid atappropriate times to complete the advancement sequence. In anotherexample, the core 1 and sheath 2 may both include a steerable tip 3providing each structure with both directional control and the momentaryrigidity necessary for shape-transference.

FIG. 3 depicts an alternative embodiment of a shape-transferring cannulasystem in accordance with the present invention. In this embodiment, theshape-transferring core 1 and sheath 2 are not necessarily coaxialstructures and may be laterally parallel structures that slidably engageeach other longitudinally via engagement features 10. In general,engagement features in accordance with the present invention includestructures that permit the core 1 and sheath 2 to slide or otherwisemove longitudinally relative to each other. One aspect of engagementfeatures in accordance with the present invention that one of the core 1and sheath 2 provides a rail for advancement of the other of the coreand sheath relative thereto.

At least one of the shape-transferring structures includes a steerabletip 3 with which to guide advancement of the system. Either or both ofthe shape-transferring structures can contain accessory lumens 11through which surgical tools may be introduced or through which thetarget site may be irrigated or suctioned. The engagement feature 10 ofeither structure can be used as a guide for withdrawing samples orinserting tools that won't fit through the accessory lumen 11. Outsizedtools may be provided with compatible engagement features such that theytrack along the guide formed by the rigidizing structure's engagementfeatures.

In a preferred embodiment of the present invention, the user's selectionof an advancement direction and his actuation of the system, whethermanual or powered, causes the entire cycle of core rigidization, sheathrelaxation, sheath advancement, sheath rigidization, and core relaxationto occur such that the structure is returned to its initial state with anew longitudinal shape.

The core and sheath structures may be unitary materials or continuousstructures that can be transformed between relatively rigid andrelatively flexible or they can be formed of individual, flexiblyconnected rigid links which become substantially locked together torigidize the structure. In an embodiment comprised of links, the sheathand core linkage structures are rigidized by temporarily preventing, byany suitable mechanism, substantial relative motion between the links.For example, motion between links may be temporarily stopped orsubstantially reduced by tightening a tension cable to put the linkageinto longitudinal compression, by electrostatic or magnetic forces, byhydraulic or pneumatic actuation, by changes in viscous coupling as withelectrorheological or magnetorheological materials, or through anyfriction modulating means.

Linkages may be held together by a flexible internal cable or externalcovering, or by attaching the links to each other while leaving enoughfreedom of rotation to make the structure longitudinally flexible. Morespecifically as shown in FIGS. 4A and 4B, the links may be looselycaptured by overlapping ball and cup features in adjacent links suchthat the cup features 22 overlap past the equators of the adjacent ballfeatures 23. This arrangement allows two-axis pivoting between linkswhile keeping the linkage intact. FIG. 4A illustrates a specific exampleof a rigidizing mechanism where sheath and core rigidizing linkagestructures may include a compression element 20 in each link, such as aloop of nickel-titanium alloy wire or shape memory polymer whoseshape-memory transition temperature is higher than normal bodytemperatures. A slot 24 in the cup 22 may facilitate compression of thecup against the ball 23 when the compression element 20 is actuated. Thecompression elements 20 in the links may be actuated through electricalor inductive heating or through any suitable means to activate theshape-memory effect such that the compression elements reduce theirunstressed diameters, creating local compression between ball and cup,and thus increasing friction between links.

FIG. 4B illustrates another example of a rigidizing mechanism employingthe same type of captured-link linkage configuration as the previousexample. In this embodiment, either the ball 23 or the cup 22 caninclude active material components 25 made of materials such aselectroactive polymer (EAP) that change shape when energized. The activematerial components may be oriented to expand radially when energized,causing interference between the ball and cup of adjacent links.Alternately, in a normally-rigid structure, the active materialcomponents 25 may be oriented to contract radially when energized,relieving interference between the ball and cup features of adjacentlinks.

By way of another example, linkages built of links made of dielectricmaterials may be rigidized electrostatically by building attractive orrepulsive charges between links and increasing friction between links.By way of another example, inducing magnetic attraction or repulsionbetween links containing ferromagnetic materials can stiffen arigidizing linkage by increasing friction between the links. By way ofanother example, linkages built with links made of conductive materialsmay be rigidized by inducing eddy currents that attract links to eachother and increase friction between links.

FIGS. 5 and 6 illustrate a linkage embodiment of parallel rigidizingsheath and core structure that employs rigidizing wires or cables 34 and40, which go through the core 1 and sheath 2 respectively. These cables,when put into tension, pull the links together to increase frictionbetween the links and thus prevent relative motion between the links.When not in tension, the rigidizing cables serve to hold the individuallinks in the rigidizing assembly together.

As illustrated in FIG. 5, the core's rigidizing structure 30 is built-upof links such that a convex spherical surface 31 on one link engages aconcave surface 32 on the adjacent link. FIG. 5 shows cup-like nestinglinks 33 with a spherical ball-joint-like interface that allows two-axispivoting between abutting links, thus making the linkage longitudinallyflexible. The core's rigidizing cable 34 runs through each core link'scentral orifice 35, connecting the entire core rigidizing structure 30.The steerable tip 3 control cables 36 may also run through each link'scentral orifice 35. The control cables 36 may be mechanical cablestransmitting tension or compression, or electrical connectionstransmitting power or signal to actuate or control the steerable tip 3.Alternatively, the rigidizing cable 34 and tip-steering cable 36 may becontained within individual lumens of a multilumen housing or withinindividual housings, keeping them separated and keeping the tip-steeringcables 36 from binding when the rigidizing cable 34 is tensioned tostiffen the core structure. The housing material may be chosen for lowfriction cable movement. One lumen of the multilumen housing might alsoserve to guide the core 1 along a conventional guidewire for rapidinsertion into guidewire accessible anatomy such as the atria andventricles of the heart.

Other linkage geometries that allow two-axis pivoting are possiblewithin the scope of this invention. For example as in FIG. 21, links 240with male 241 and female 242 pivot features that each rotate on only oneaxis can be alternated and mounted within each other, within therigidizing structure, with adjacent pivot features having axesperpendicular to one another. Thus, each pair of links 240 provides twoorthogonal pivoting axes to the linkage structure.

FIG. 6 illustrates a linkage embodiment of the sheath 2 in which thesheath links include a hollow central orifice 41 and pivot on sphericalball-joint like ball 48 and cup 47 surfaces for two-axis pivoting. Thesheath's rigidizing cable 40 runs outside each sheath 2 link's centralorifice 41 allowing the assembled links to form a hollow central lumen42 that can be occupied by the core 1 structure during cannulaadvancement as well as by items such as surgical instruments which thesheath lumen 42 can guide to a surgical or diagnostic site. The link'scentral orifice 41 has a diameter D2 that is substantially similar todiameter D1, described above.

The rigidizing sheath links 45 may include at least two cable-guidingfeatures 44 external to the central lumen 42. The cable 40 andcable-guiding features 44 are configured for low friction sliding.Friction may be further reduced by encasing the cable in a cable housingformed of a material with low-friction properties, such as PTFE, HDPE,and the like, thus separating it from the cable-guiding features 44.Alternatively, the cable-guiding features themselves could bemanufactured from low friction materials different from that of the restof the links. When the links 45 are assembled into a rigidizingstructure 46, the cable-guiding features 44 form segmented channelsrunning the length of the rigidizing structure 46. Since the cables 40do not run down the central axis of the sheath 2, cables running onopposite sides of the sheath 2 must effectively change length when thesheath 2 bends. Cable segments closer to the center of curvaturerelative to the structure's neutral axis will have to shorten. Likewise,cable segments further from the center of curvature relative to thesheath's 2 neutral axis will have to lengthen.

An embodiment of a linkage sheath with two cable-guiding channels anequal radial distance from the sheath's central axis may employ thesingle cable 40 wrapping around a pulley 43, which may be a rotatingcomponent, sliding surface, or the like, to run back and forth along thelength of both cable-guiding channels. As the structure bends, the innercable path will shorten the same amount as the outer cable pathlengthens and cable length will move from the shortening side around thepulley 43 to the lengthening side. Tension on the pulley 43 with respectto the linkage structure 46 tightens the entire cable 40 and stiffensthe sheath 2 by increasing friction between the links. Referring to FIG.7, the sheath's tensioning pulley 43 may be positioned off-axis suchthat the sheath central lumen 42 is clear and able to receive the core 1or surgical instruments. A cable-guiding element 50 at the base of thesheath 2 acts to redirect the tensioning cable 40 to an off-axis pulley43 and away from the sheath's central lumen 42.

Referring to FIG. 8, the sheath rigidizing linkage structure 60 may runparallel to the core 1 without being coaxial with it. Each link mayinclude dedicated rigidizing features 61 through which a rigidizingcable 62 may run and at least one lateral orifice 62 which, whenmultiply assembled in the complete linkage, form a laterally parallelsegmented lumen through which the core 1 or surgical tools may run. Thelateral orifice 62 has a diameter D3, which is substantially similar todiameter D1, described above.

FIG. 9 depicts a laterally parallel sheath linkage. The laterallyparallel sheath 60 a may form a lateral lumen 70 capable of formingvarying radii of curvature by nesting conical shapes that form thelateral lumen 70, leaving sufficient mechanical clearance 71 toaccommodate an angle .alpha. between adjacent links. The angle .alpha.is preferably in the range from about zero degrees to about 90 degrees.The lateral lumen diameter D4 is substantially similar to diameter D1,described above.

FIG. 10 depicts an alternate embodiment of a linkage. Linkage 82 withthe parallel lateral lumen 70 may include an open side 80 such thatobjects 81 larger than the lumen diameter D4 may be introduced to andwithdrawn from the surgical or diagnostic site using the combinations ofthe open sides 80 to retain therein a matching portion 83 on the object81.

FIG. 11 depicts another alternate embodiment of a linkage. Linkage 82 awith the parallel lateral lumen 70 may employ flexible elements 90 inthe lumen portion of each link that partially overlap each adjacentlink. The flexible elements serve to form a smoother and largersegmented lumen than would be formed by purely rigid links by flexingwhen formed into a radius rather than requiring clearance for the entirerange of motion between the links.

Referring to FIGS. 12A-12G, a mechanism for advancing parallelrigidizing elements may include two opposing racks 91 and 92 thatalternatingly advance relative to each other. Referring to FIG. 12G, themaximum amount of incremental advancement, length ‘1’, is ideallylimited to the length of cannula having the steerable tip 3. A linearlysliding shuttle 93 supports one rack and a housing 94 supports the otherrack. The core actuation handle 95 (not shown for clarity in FIG. 12Aand FIG. 12B) and core rack 91 are each pivotally attached to thehousing 94. The sheath actuation handle 96 and sheath rack 92 are eachpivotally attached to the shuttle 93. The core and sheath actuationhandles 95 and 96 are attached to the rigidizing cables 40 and 34 of thesheath 2 and core 1, respectively. Upon actuation by the user, thesehandles rotate on their pivots 97 and 98 to first relax their respectiverigidizing structure, disengage their respective rack from the other,which remains temporarily fixed, and transmit the force which slides thehousing 94 and shuttle 93 with respect to one another to advance theshape-transferring cannula.

Beginning the advancement sequence as shown in FIG. 12B, spreading thehandholds 99 and 100 (core advancement handhold 99 not shown forclarity) apart biases the core handle 95 (not shown for clarity) againstits mechanical stop 104 in the housing 94 and rotates the sheath handle96 on its pivot 98, first compressing the sheath rigidizing spring 106,relaxing the sheath linkage 2, and then disengaging the sheath rack 92from the currently-fixed core rack 91. The sheath rack 92 disengages thecore rack 91 by rotating on its pivot 105 against the force of thesheath rack bias spring 113. The sheath rack 92 is rotated away from thecore rack 91 by the force of the sheath rack lifter 115, which extendsfrom the sheath handle 96, acting against the rack's lift tab 117. Aninitial gap between the sheath rack lifter 115 and rack's lift tab 117allows the sheath handle 96 to rotate enough to compress the sheathrigidizing spring 106 and relax the sheath 2 before the sheath rack 92is disengaged from the core rack 91. As illustrated in FIG. 12C,continued spreading of the actuation handles 95 and 96, with racks 91and 92 disengaged, translates the handles apart from each other andadvances the shuttle 93 and sheath 2 relative to the housing 94 and core1.

As illustrated in FIG. 12D, releasing the handle spreading pressureallows the sheath rigidizing spring 106 to rotate the sheath handle 96back to its resting position and re-stiffen the sheath 2 by tensioningthe sheath rigidizing cable 40. The rotation of the sheath handle 96, inturn, rotates the sheath rack lifter 115 away from the sheath rack 92,allowing the sheath rack bias spring 113 to rotate the sheath rack 92towards the core rack 91. Re-engagement of the racks locks the mechanismin a sheath-forward position shown in FIG. 12D.

Continuing the advancement sequence as shown in FIG. 12E, squeezing theadvancement handholds 99 and 100 of the actuation handles 95 and 96 suchthat they rotate towards each other biases the sheath handle 96 solidlyagainst its mechanical stop 101 on the shuttle 93 and rotates the corehandle 95 on its pivot 97, first compressing the core rigidizing spring102, relaxing the core linkage 1, and then disengaging the core rack 91from the currently-fixed sheath rack 92. The core rack 91 disengages thesheath rack 92 by rotating on its pivot 103 against the force of thecore rack bias spring 112. The core rack 91 is rotated away from thesheath rack 92 by the force of the core rack lifter 114, which extendsfrom the core handle 95, acting against the rack's lift tab 116. Aninitial gap between the lifter 114 and lift tab 116 allows the corehandle 95 to rotate enough to compress the core rigidizing spring 102and relax the core 1 before the core rack 91 is disengaged from thesheath rack 92. The racks 91 and 92 being disengaged from each other,continued squeezing as shown in FIG. 12F translates the handles 95 and96 closer together by advancing the housing 94 and core 1 relative tothe shuttle 93 and sheath 2.

Releasing the squeezing pressure on the advancement handholds 99 and 100allows the core rigidizing spring 102 to rotate the core handle 95 backto its resting position and re-stiffen the core 1 by tensioning the corerigidizing cable 34. The rotation of the core handle, in turn, rotatesthe core rack lifter 114 away from the core rack 91 allowing the corerack bias spring 112 to rotate the core rack 91 towards the sheath rack92. Re-engagement of the racks locks the mechanism in the sheath-backposition shown on FIG. 12A.

Referring to FIG. 12G, the difference in engaged length of the racks 91and 92 between the sheath-back position and the sheath-forward position,length ‘L’, as well as the position of the sliding stop structures 110and 111 in the housing 94 and shuttle 93 define the maximum relativemotion for incremental advancement between the sheath 2 and core 1elements. The amount of incremental advancement, length ‘L’, ispreferably limited to the length of the steerable tip 3. Rack features107 such as teeth define the increments in which the shape-transferringcannula may be mechanically advanced or retracted. The rack features 107may be configured to allow only integral advancement of units the lengthof the entire steerable tip 3 as shown in FIG. 12G or, alternately, maybe configured allow units of advancement fractions of that length.

The rack mechanism described above may also withdraw theshape-transferring cannula in controlled increments through a processreversing the advancement sequence. Withdrawal of hand-holds 108 and 109on the ends of the handles 95 and 96 opposite the advancement endsactuate the mechanism in reverse using the same gripping and spreadingfinger/thumb motions used to advance the cannula.

In another embodiment of the invention, FIGS. 20A and 20B depictrigidizing structures including inner and outer concentric tubes, 221and 222 respectively, separated by short segments of materials 223 thatchange shape when energized, such as electroactive polymer (EAP), whichchanges shape when exposed to electric fields. The inner tube 221 mayormay not have an open lumen. When employing biaxially active materialssuch as EAP, the active material components are oriented to contractlongitudinally and expand radially when energized. The active materialcomponents may be employed in a normally-noninterfering configuration ora normally-interfering configuration. In a normally-non-interferingconfiguration the active material components 223 are each attached toone of the concentric tubes 221 or 222 such that they do not contact theother tube, as shown in FIG. 20A, when not energized. When energized,the radial expansion of the active material components 223 causesmechanical interference with the other tube, as in FIG. 20B, thuspreventing motion between the opposed surfaces 224 and 225 andeffectively locking-in the curvature of the rigidizing structure.According to the present invention, one may substitute materials thatchange shape when exposed to electric current, magnetic fields, light,or other energy sources. The same rigidizing effect may be achieved byreplacing normally-non-interfering active material components 223 withnon-interfering balloons expandable by gas or liquid fluid pressure.Alternately, such materials may be placed in a normally-interferingconfiguration between concentric tubes 221 and 222 such that theyinterfere, as in FIG. 20B when not energized and contract radially tothe state depicted in FIG. 20A when energized. For example, anormally-rigid structure made stiff by normally-interfering EAPcomponents 223 may be made flexible by applying a voltage to the EAPcomponents such that they contract radially to the noninterfering statedepicted in FIG. 20A, relieving the mechanical interference and allowingrelative motion between the opposed surfaces 224 and 225 of theconcentric tubes 221 and 222. Similarly, normally-interfering balloonsreplacing normally-interfering active material components 223 may becollapsed by applying a relative vacuum.

Referring to FIG. 13A, in an alternate embodiment of the invention, therigidizing sheath 2 can include rotating wedge links 130. The wedgelinks 130 have hollow central axes 131 that form the sheath's lumen 42as well as two interface features 132 angled with respect to oneanother. For example, the angle between the links can be between aboutzero degrees and about 90 degrees. The perpendicular centerlines 133 ofthe interface surfaces define axes of rotation between the links. Asdepicted diagrammatically in FIGS. 13B and 13C, the wedge links 130 in asample starting position in FIG. 13B rotate with respect to neighboringlinks 134 at the connecting interface 132 between links. This rotationforms curves as shown in FIG. 13C in the sheath 2 structure whilemaintaining a substantially constant sheath lumen 42 volume. Impedingrotation between links rigidizes the structure. Link rotation can beprevented through any of the ways described above for impeding relativemotion between links. The wedge links 130 may be formed as sections ofspheres as shown in FIG. 13A to avoid creating sharp corners when curvesare formed, leaving a relatively smooth and atraumatic outer surface.

FIGS. 14A-14C depict another embodiment of the invention in which one ofthe two parallel elements in the shape-transferring cannula is passive.The passive element is more rigid than the relaxed rigidizing structureand more flexible than the stiffened rigidizing structure. The passiveelement is less mechanically complex than an equivalent rigidizingstructure, not requiring rigidizing cables 34 and 40 or other mechanismsto serve the shape-transfer function. Thus a shaped cannula assemblywith a passive sheath may be narrower in cross-section than an assemblyformed of two rigidizing structures. In FIG. 14A the core 1 is relaxedsuch that it is more flexible than the sheath 2 and has been advancedsuch that the steerable tip 3 protrudes ahead of the sheath 2. In FIG.14B the core 1 is stiffened such that it is more rigid than the sheath 2and the user deflects the steerable tip 3 towards the direction ofintended cannula advancement. In FIG. 14C the core 1 remains stiffenedsuch that it is more rigid than the sheath 2 and the sheath is thenadvanced over the core and its steerable tip 3. The sheath 2 assumes thecore's longitudinal shape including the new bend introduced by the userthrough the deflected steerable tip 3. Elements of a passive linkstructure could be mechanically energized to encourage them to moverelative to one another when being advanced past a relatively rigidstructure. Mechanical energizing can be achieved by vibrating thepassive structure with any suitable device, such as a piezoelectrictransducer, voicecoil, or eccentrically weighted motor.

Embodiments of the invention that employ continuous, non-segmented,parallel core and sheath structures can be made smaller in cross-sectionthan mechanically-stiffened linkage structures. Such structures may beconstructed such that they become relatively rigid when energized orbecome relatively flexible when energized.

FIG. 15 depicts a continuous, parallel shape-transferring core andsheath structure. The core 1 and sheath 2 structures can each includeinner 151 and outer 152 flexible tubes containing stiffening material153 that increases in viscosity or otherwise stiffens when energized.Examples of such substances are electrorheological fluid, which stiffensupon exposure to electrical potential, and magnetorheological fluid,which stiffens upon exposure to magnetic fields. A rigidizing structureconfigured as a core or as a sheath may be built-up of inner 151 andouter 152 containment tubes with stiffening material 153 sandwiched inbetween. In the case of a core, the inner tube may be a solid elementsuch as plastic monofilament, lacking a lumen. In the case of astructure employing electrorheological fluid, flexible electricalcontacts may line the length of each containment tube or the tube itselfmay be made of electrically-conductive plastic or other similarmaterial. A section of electrically insulating material 154 may connectthe tubes 151 and 152 at their proximal and distal ends, mechanicallyconnecting the tubes 151 and 152 and sealing the electrorheologicalfluid within. A woven mesh or other similar separating material 155sandwiched with the electrorheological fluid between the tubes 151 and152 may act as a baffle, restricting the flow of viscous fluid so as toincrease the rigidity of the structure when energized, and as aninsulator when an electrical potential is used to energize the elements.The tubes 151 and 152 themselves may contain baffling features such asgrooves or threads and may also contain a layer of insulating material,obviating the need for a separating material 155. A similar structureemploying magnetorheological fluid could be constructed with at leastone containment tube containing electrical conductors arranged in such amanner as to generate a magnetic field sufficient to rigidize thestructure.

A shape-transferring cannula structure may be constructed ofnormally-rigid core 1 and sheath 2 elements which, in proper sequence,become flexible when energized and re-stiffen when they return to anun-energized state. Each element can become flexible enough, whenenergized, to be advanced along a relatively rigid mating structure andthen, when de-energized, become rigid enough to mechanically support theadvancement of an energized parallel structure. Referring to FIG. 16,parallel normally-rigid core 1 and sheath 2 elements may include intheir construction thermoplastic, thermoplastic alloys such as Kydex™(acrylic-PVC alloy), urethane alloys, or similar materials that softento a flexible state when heated above a transition temperature byembedded heating elements 171 and 172 or any suitable mechanism. Thetransition temperature can be selected through design and materialcomposition to be somewhat higher than normal body temperatures. Thenormally-rigid parallel structures may contain heating elements thatmomentarily increase their temperatures above the flexibility transitiontemperature. Surrounding body fluid such as blood, saline solution, orlymph can serve as a heat sink to quickly draw heat away and re-stiffenthe structures when the momentary heating is ceased. Similarly, as shownin FIG. 23, normally-rigid core 1 or sheath 2 structure can include aguidewire 260 with wirewound coils in its construction. The coils 263can be at least partially potted in a low-temperature flowing material261 such as wax or polymer which adheres to the coils. Thelow-temperature flowing material 261 may be contained within a compliantcover 262. In an un-energized state the flowing material 261 isrelatively solid and prevents the coils 263 from moving substantiallywith respect to one another, thus substantially locking-in the curvatureof the structure. When energized through heating, the flowing material261 softens sufficiently to allow relative motion between coils 263,thus relaxing the structure.

Referring to FIGS. 19A and 19B, shape-transferring cannula can be builtof normally-rigid core 1 and sheath 2 structures, each includingflexible tubes 212 and 214 respectively, containing substantially stiffmaterials 213 that relax upon vibration. Such materials can includeinterlocking particles like sand grains or normally-viscous fluid, suchas xanthan gum that becomes less viscous upon agitation. Vibrating eachstructure, for example with a vibrating element 215 such as apiezoelectric transducer, a voicecoil, or a motor with an eccentricallymounted weight, could temporarily relax it to a flexible state byloosening the interlocking particles or by causing the contained fluidto transition to a less viscous state. Alternatively, the containmenttubes 212 and 214 themselves could be constructed of or contain apiezoelectric material such as PVDF (polyvinylidene fluoride) alongtheir length such that each entire tube could actively vibrate whenenergized with an alternating voltage V.

In another embodiment of the invention, FIGS. 20A and 20B depictrigidizing structures including inner and outer concentric tubes, 221and 222 respectively, separated by short segments of materials 223 thatchange shape when energized, such as electroactive polymer (EAP), whichchanges shape when exposed to electric fields. The inner tube 221 mayormay not have an open lumen. When employing biaxially active materialssuch as EAP, the active material components are oriented to contractlongitudinally and expand radially when energized. The active materialcomponents may be employed in a normally-noninterfering configuration ora normally-interfering configuration. In a normally-non-interferingconfiguration the active material components 223 are each attached toone of the concentric tubes 221 or 222 such that they do not contact theother tube, as shown in FIG. 20A, when not energized. When energized,the radial expansion of the active material components 223 causesmechanical interference with the other tube, as illustrated in FIG. 20B,thus inhibiting or preventing motion between the opposed surfaces 224and 225 and effectively locking-in the curvature of the rigidizingstructure. The same invention may substitute materials that change shapewhen exposed to electric current, magnetic fields, light, or otherenergy sources. The same rigidizing effect may be achieved by replacingnormally-non-interfering active material components 223 withnon-interfering balloons expandable by gas or liquid fluid pressure.Alternately, such materials may be placed in a normally-interferingconfiguration between concentric tubes 221 and 222 such that theyinterfere, as in FIG. 20B when not energized and contract radially tothe state depicted in FIG. 20A when energized. For example, anormally-rigid structure made stiff by normally-interfering EAPcomponents 223 may be made flexible by applying a voltage to the EAPcomponents such that they contract radially to the non-interfering statedepicted in FIG. 20A, relieving the mechanical interference and allowingrelative motion between the opposed surfaces 224 and 225 of theconcentric tubes 221 and 222. Similarly, normally-interfering balloonsreplacing normally-interfering active material components 223 may becollapsed by applying a relative vacuum.

Referring to FIG. 17A, core and sheath rigidizing 180 structures caninclude compliant inner and outer tubes, 181 and 182, containingcompression-stiffening particles 183 in the annular space between theopposing tube surfaces. The compression stiffening particles 183 aremade of materials such as expanded polystyrene that interlock and form asubstantially rigid structure when compressed. Such compression canoccur when the space containing the compression-stiffening particles isplaced under a relative vacuum P. Alternatively, external pressure maybe applied to the material in the annular inter-tubal space to compressand stiffen it. For example, pressure may be applied to the internalconcentric tube such that it expands and presses compression-stiffeningmaterial in the inter-tube space against the external concentric tube.Referring to FIG. 17B, core 1 structure can include a compliant tube 184containing compression-stiffening particles 183. The structure may bestiffened by putting the tube's interior under relative vacuum P.

Referring to FIG. 18, a core 1 or sheath 2 structure including links 191may be rigidized or relaxed via pressure P which can be either positivepressure or relative vacuum. In a normally-rigid configuration, acompliant cover 192 the length of the structure can be stretched tautagainst the movable links 191 in an equalized pressure environment. Thetight covering 192 keeps the links from moving substantially relative toone another, making the rigidizing structure stiff. Application ofpressure P underneath the compliant cover 192 expands the cover,allowing the links 191 to rotate relative to one another therebyrelaxing the structure. Alternately, in a normally-flexible structure,the compliant cover 192 can loosely cover the links 191 in an equalizedpressure environment such that the links can rotate relative to oneanother. Applying a relative vacuum P inside the compliant cover 192causes it to compress against the movable links 191, preventing theirrotation relative to one another thereby stiffening the structure.

The rigidizing structures described above as a paired system may be alsoemployed singly as an alternatingly rigid and compliant support for asteerable catheter such as an endovascular catheter or flexibleendoscope. In such cases as depicted in FIG. 22, the rigidized structureprovides support for the catheter to round corners without thepossibility of looping because the flexible element is advanced onlywhen the supporting structure is rigid. Similarly, the relaxedrigidizing support is advanced only along the length of the catheter,using it as a guidewire.

In another embodiment of the invention, a steerable catheter such as anendovascular catheter or flexible endoscope may be aided in advancingaround tight corners through alternating between advancement of twoparallel structures, using the relatively rigid steerable bendingsection at the tip to advance through a tight anatomical turn withoutlooping.

In one embodiment, the sheath is rigidized and the core with anarticulating tip is made flexible. The core is advanced and thenrigidized. The articulating tip is pointed in the desired direction ofpath creation. The sheath is relaxed and advanced over the rigid core.

Referring now to FIG. 24, yet further aspects of the present inventionare illustrated. More specifically, FIG. 24 illustrates that thehandholds, such as handholds 99, 100, 108, 109 illustrated in FIGS.12A-12H, can optionally be replaced with a semi- or fully automatedsystems, to permit the practitioner's hands to be used for other tasksduring the particular procedure performed on a patient. As illustratedin FIG. 24, a rack 302 having teeth 304 is pivotally mounted to the arm306 at a pivot 308, to which handhold 100 is attached in the embodimentillustrated in FIG. 12G. A pinion 310 having teeth 316, which mate withteeth 304, is rotatably mounted to arm 312, while a pin or the like 314holds the rack 302 against the pinion. Thus, rotation of pinion 310,such as by a rotary motor 318 or the like, causes arm 306 to move indirection X, while the arm 312 can be separately or simultaneously movedalong direction X by pulling or pushing on the arm 312, or the motor318, with a suitable linear actuator or motor (not illustrated). Furtheroptionally, the activation of the actuators or motors, including motor318, can be automated by controlling them using an automatic controller320. By way of example and not of limitation, controller 320 can be ageneral purpose computer having a memory 322 in which the logic of thesequence of movements of the arms 306, 312 can reside. Alternatively,controller 320 can be a PLC controller or other controller as will bereadily appreciated by those of skill in the art, which canautomatically control the movements of the arms 306, 312.

While the invention has been described in detail with reference topreferred embodiments thereof, it will be apparent to one skilled in theart that various changes can be made, and equivalents employed, withoutdeparting from the scope of the invention. Each of the aforementioneddocuments is incorporated by reference herein in its entirety.

What is claimed is:
 1. A method for advancing a rigidizable medicaldevice, the method comprising: rigidizing a portion of an outer elementof the device; while the portion of the outer element is rigidized,advancing an inner element of the device relative to the outer elementof the device by a first preestablished length of advancement; afteradvancing the inner element, relaxing the portion of the outer elementof the device; and after relaxing the portion of the outer element,advancing the outer element of the device relative to the inner elementof the device by a second preestablished length of advancement.
 2. Themethod of claim 1, further comprising rigidizing a portion of the innerelement of the device; while the portion of the inner element isrigidized, advancing the outer element of the device relative to theinner element of the device by the second preestablished length ofadvancement; and after advancing the outer element, relaxing the portionof the inner element of the device.
 3. The method of claim 1, furthercomprising maintaining an overlap between the outer element of thedevice and the inner element of the device.
 4. The method of claim 3,wherein the inner element comprises a steerable region, and whereinmaintaining the overlap comprises maintaining an overlap of the outerelement of the device and at least a portion of the steerable region. 5.The method of claim 4, wherein maintaining the overlap comprises settingeach of the first and second preestablished lengths of advancement to alength that is less than or equal to a length of the steerable region ofthe inner element of the device.
 6. The method of claim 1, wherein therigidizing the portion of the outer element comprises applying tensionto one or more cables coupled to the outer element.
 7. The method claim1, wherein the inner element comprises a core and the outer elementcomprises a sheath.
 8. The method claim 1, wherein the inner elementcomprises an insertable device and the outer element comprises acannula.
 9. The method of claim 8, wherein the advancing the outerelement comprises advancing the cannula into a hollow body structure.10. The method of claim 9, wherein the advancing the outer elementcomprises advancing the cannula into a colon.
 11. The method of claim 9,wherein the advancing the outer element comprises advancing the cannulathrough a blood vessel.
 12. The method of claim 1, wherein the advancingthe rigidizable medical device accompanies an endoscopic procedure. 13.The method of claim 1, wherein the medical device is a core of a cannulasystem.
 14. The method of claim 1, wherein the medical device is asheath of a cannula system.
 15. A method for advancing a cannula systeminto a body, the method comprising: inserting a device through acannula; after inserting the device, rigidizing a portion of thecannula; while the portion of the cannula is rigidized, advancing thedevice through the cannula until a first preestablished length ofadvancement; after advancing the device, relaxing the portion of thecannula; and while the portion of the device is relaxed, advancing thecannula until a second preestablished length of advancement, wherein thefirst and second preestablished lengths of advancement maintain anoverlap between the cannula and at least a portion of a steerable regionof the device.
 16. The method of claim 15, wherein each of thepreestablished lengths of advancement is set to a length that is lessthan or equal to a length of the steerable region of the device.
 17. Themethod of claim 15, wherein the advancing the cannula system comprisesadvancing the cannula system into a hollow body structure.
 18. Themethod of claim 15, wherein the advancing the cannula system accompaniesan endoscopic procedure.